The Woodlands, Texas, September 15, 2009 – Lexicon Pharmaceuticals, Inc. (Nasdaq: LXRX), a biopharmaceutical company focused on discovering breakthrough treatments for human disease, obtained favorable results from recently completed Phase 1 studies of LX4211 and announced today that it has initiated a Phase 2 clinical trial of the drug candidate in patients with type 2 diabetes mellitus. LX4211 is an orally-delivered, small molecule drug candidate that inhibits the sodium glucose transporter 2 (SGLT2). LX4211 is Lexicon’s fourth drug candidate currently being tested in Phase 2 clinical trials.

“LX4211 offers an opportunity to treat diabetes by increasing urinary glucose excretion through a mechanism of action that is expected to avoid some of the disadvantages of existing diabetes drugs that result in storage of excess glucose,” said Brian P. Zambrowicz, Ph.D., executive vice president and chief scientific officer at Lexicon. “By contrast, LX4211 through inhibition of SGLT2 has the potential to reduce caloric load and thereby enhance overall glucose homeostasis in patients with type 2 diabetes.”

In the recently completed Phase 1 clinical trial in normal healthy volunteers, LX4211 was well tolerated at all dose levels and produced a dose-dependent increase in urinary glucose excretion. LX4211 also demonstrated a favorable pharmacokinetic profile supporting the potential for once daily dosing. Adverse events were generally mild and were distributed across all dose groups, including the placebo group.

Based on the Phase 1 clinical results, Lexicon has initiated a Phase 2 clinical trial to evaluate the safety and tolerability of two dose levels of LX4211 and its effect on diabetes biomarkers including: fasting blood glucose, urinary glucose excretion and response to oral glucose tolerance testing in patients with type 2 diabetes. The four-week, randomized, double-blind, placebo-controlled study will be conducted in the United States and is expected to enroll 36 patients with type 2 diabetes.

In addition to LX4211, Lexicon has three other drug candidates progressing in Phase 2 clinical trials: LX1031 for irritable bowel syndrome, LX1032 for carcinoid syndrome and LX2931 for rheumatoid arthritis. For more information about Lexicon’s clinical development programs, please visit www.lexpharma.com.

About the Target
LX4211 was developed at Lexicon as a potent inhibitor of the sodium glucose transporter 2 (SGLT2), a transporter responsible for the majority of glucose reabsorption by the kidneys. Lexicon found that mouse knockouts engineered to lack the SGLT2 gene are healthy and require less insulin to manage a glucose challenge. Compounds developed by Lexicon that inhibit SGLT2 may potentially treat diabetes by increasing urinary glucose excretion, thereby lowering blood glucose levels as well as caloric load.

About Diabetes
Diabetes mellitus is a common metabolic disorder associated with abnormally high blood sugar levels. Diabetes is classified as either type 1, which is characterized by severely diminished insulin production, or type 2, which is characterized by moderately diminished insulin production in conjunction with insulin resistance (insensitivity of the tissues of the body to insulin). Insulin is a hormone that regulates blood glucose levels. Diabetes can seriously impair overall quality of life and may lead to multiple complications including heart disease, stroke, and kidney failure. According to the International Diabetes Federation, more than 245 million people have diabetes, with type 2 diabetes being the most prevalent.

About Lexicon
Lexicon is a biopharmaceutical company focused on discovering breakthrough treatments for human disease. Lexicon currently has five drug candidates in development for autoimmune disease, carcinoid syndrome, diabetes, glaucoma and irritable bowel syndrome, all of which were discovered by the company’s research team. The company has used its proprietary gene knockout technology to identify more than 100 promising drug targets. Lexicon has focused drug discovery efforts on these biologically-validated targets to create its extensive pipeline of clinical and preclinical programs. For additional information about Lexicon and its programs, please visit www.lexpharma.com.
Safe Harbor StatementThis press release contains “forward-looking statements,” including statements relating to Lexicon’s clinical development of LX4211 and the potential therapeutic and commercial potential of LX4211. This press release also contains forward-looking statements relating to Lexicon’s growth and future operating results, discovery and development of products, strategic alliances and intellectual property, as well as other matters that are not historical facts or information. All forward-looking statements are based on management’s current assumptions and expectations and involve risks, uncertainties and other important factors, specifically including those relating to Lexicon’s ability to successfully conduct clinical development of LX4211 and preclinical and clinical development of its other potential drug candidates, advance additional candidates into preclinical and clinical development, obtain necessary regulatory approvals, achieve its operational objectives, obtain patent protection for its discoveries and establish strategic alliances, as well as additional factors relating to manufacturing, intellectual property rights, and the therapeutic or commercial value of its drug candidates, that may cause Lexicon’s actual results to be materially different from any future results expressed or implied by such forward-looking statements. Information identifying such important factors is contained under “Factors Affecting Forward-Looking Statements” and “Risk Factors” in Lexicon’s annual report on Form 10-K for the year ended December 31, 2008, as filed with the Securities and Exchange Commission. Lexicon undertakes no obligation to update or revise any such forward-looking statements, whether as a result of new information, future events or otherwise.

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